v3.9.4

Optimization v3.9.4

Diff since v3.9.3

Closed issues:

• Reuse of Ipopt.Optimizer() errors (#347)
• Error when using callback function and Ipopt (#421)
• Make sure that all values are Float64 else AmplWriter fails (#422)

Merged pull requests:

• Use updated ordering from toexpr in constraint expression (#424) (@Vaibhavdixit02)
• Disallow callback in MOI subpackage and empty solver if prepopulated (#426) (@Vaibhavdixit02)
• lib cov (#427) (@ArnoStrouwen)
• track only src (#428) (@ArnoStrouwen)